As a high performance rare earth sintered magnet, two kinds of magnets, i.e., a samarium-cobalt-based sintered magnet and a neodymium-iron-boron-based sintered magnet are widely used.
Especially since the neodymium-iron-boron-based sintered magnet (“R-T-B-based sintered magnet, hereinafter) shows the highest magnetic energy product among various magnets and is inexpensive and thus, this magnet is employed in various kinds of electric equipment.
A rare earth sintered magnet such as the R-T-B-based sintered magnet is produced in a manner that raw material metal is melted, alloy powder formed by roughly pulverizing and finely pulverizing raw material alloy obtained by pouring the raw material metal into a mold or raw material alloy formed by a strip casting method is press-formed and then, the press-formed resultant matter is subjected to a sintering step and a thermally processing step. As the press forming method, there are known two kinds of methods, i.e., a dry molding method in which the pressing and forming operation is carried out using dry alloy powder, and a wet molding method (registered trademark: HILOP, patent document 1, patent document 2) in which alloy powder before molding is put into oil to form slurry, and the molding is carried out using this slurry. In any of the dry molding method and the wet molding method, a molded body becomes chipped or cracked during the molding operation or due to a handling manner after the molding operation, and defective molded bodies are generated. Further, in the case of rare earth metal used for a rare earth sintered magnet, since countries of origin are limited, a supply amount is limited and the rare earth metal is expensive. Hence, to suppress the producing cost of the rare earth sintered magnet, it is absolutely necessary to reuse the defective molded bodies and recycle the same as a product.
Patent document 3 proposes a technique in which a scrap magnet is pulverized, molded and sintered to obtain a recycled magnet, metal atoms such as Dy and Tb are made to adhere to a surface of the recycled magnet, the adhered metal atoms are dispersed to crystal grain boundary and/or crystal grain boundary phase, and a scrap magnet is recycled.
Patent document 4 proposes a method of producing a rare earth sintered magnet by hydrogen-pulverizing, molding and sintering a scrap magnet having a content of oxygen generated in a producing step of a rare earth sintered magnet is 2,000 ppm or lower.
However, the above-described conventional producing methods relate to a method of recycling a sintered body or a molded body produced by the dry molding method, and these methods do not disclose a technique for recycling a molded body molded by the wet molding method.